The goal of this development project is to develop a peptide-peptide nucleic acid (P-PNA) conjugate that specifically recognizes a spliced form of an mRNA molecule produced during the Unfolded Protein Response (UPR). This development project will test the novel hypothesis that the Unfolded Protein Response is activated in tumor cells and contributes to the survival of tumor cells, particularly under hypoxic conditions experienced by cells within a rapidly growing tumor. To test this hypothesis, we will construct and characterize a peptide-peptide nucleic acid molecule (P-PNA) designed to specifically recognize a novel mRNA encoding the XBP-1 transcription factor. The mRNA encoding the XBP-1 transcription factor is both induced at the transcriptional level during the UPR and undergoes a novel UPR-dependent splicing event that results in the expression of a highly active form of XBP-1. The active form of XBP-1, in turn, activates transcription of a number of genes that both increase the folding and secretory capacity of the ER and contribute to cell survival following stresses that perturb protein folding in the ER. A radiolabeled P-PNA molecule that specifically recognizes the spliced form of XBP-1 may provide a novel approach to the imaging of incipient tumors and, by interfering with expression of the active XBP-1 protein, block a cell survival pathway that may contribute to the survival of tumor cells under hypoxic conditions. Aim 1. To synthesize a peptide-peptide nucleic acid (P-PNA)-based targeting molecule that contains the anti-sense sequence to a novel spliced form of XBP-1-encoding mRNA generated during the Unfolded Protein Response. Aim 2. To characterize the ability of the P-PNA molecule to specifically recognize the spliced form of the XBP-1 mRNA molecule both in vitro and in cultured cells.